It is generally known that a commercially important alkenylbenzene, namely styrene, is prepared by dehydrogenation of ethylbenzene in the presence of a catalyst based on iron oxide.
U.S. Pat. No. 4,467,046, issued Aug. 21, 1984, describes a dehydrogenation catalyst containing 15% to 30% K.sub.2 O, 2% to 8% CeO.sub.2, 1.5% to 6% MoO.sub.3, 1% to 4% CaCO.sub.3, the balance being Fe.sub.2 O.sub.3. The very high K.sub.2 O content and the presence of not less than four metal promoters are disadvantages of this known catalyst.
U.S. Pat. No. 4,460,706, issued July 17, 1984 describes a dehydrogenation catalyst containing 1.5% to 40% by weight of K.sub.2 O, 11 to 50% by weight of Ce.sub.2 O.sub.3 (which is equivalent to 11.5% to 52.4% by weight of CeO.sub.2), 40% to 87.5% by weight of Fe.sub.2 O.sub.3 and not over 25% by weight of calcium. The very high cerium content is a disadvantage of this known catalyst.
British Patent Specification No. 1,460,762, published Jan. 6, 1977, describes a dehydrogenation catalyst containing 1 to 40% by weight of an alkali metal compound, 0.5 to 10% by weight of cerium oxide, 5 to 30% by weight of a hydraulic cement as a binding agent, the balance being iron oxide. As hydraulic cement Portland cement may be used.
U.S. Pat. No. 3,223,743, issued Dec. 14, 1965, describes the use of two catalyst layers, one of which contains K or Ca and also Ce.
Japanese Patent Application Publication No. 59,216,634 published Dec. 6, 1984, discloses the use of dehydrogenation catalysts containing a) Mg and Ca and b) Ce and Mo.
German Patent No. DE 3,442,636 Al, published May 22, 1986 describes a dehydrogenation catalyst prepared by kneading a water-containing mixture of (a) 40-90 % wt Fe.sub.2 O.sub.3 ; (b) 5-40 % wt K.sub.2 O; (c) 3-30 % wt MgO; (d) 0-10 % wt Cr.sub.2 O.sub.3 or Mn.sub.2 O.sub.3; (e) 0-10 % wt Ce, Mo or W oxide and (f) 0-15 % wt CaO.
It has now been found that a dehydrogenation catalyst containing only three promoters and a limited amount of a cerium compound and which does not need to contain molybdenum is extremely stable.